1. Field of the Invention
The present invention relates to a method for manufacturing a light emitting device which has a highly stable light emitting element and in which the influence of variations in the light emitting element is reduced.
2. Description of the Related Art
A display device using a light emitting element has the advantage of a wide viewing angle, high-speed response, low power consumption, or the like over that having a liquid crystal layer, and it is under development.
A short circuit occurs in some cases in a portion between electrodes included in the element depending on manufacturing conditions. Then, electric current flows intensively into the short circuit portion. At this time, a current does not flow to other regions and the light emitting element is put into a non-light-emitting state as a whole, which results in a defect.
A method is therefore proposed which does not damage a normal portion of the element when dielectric breakdown occurs in advance in a defective portion of an organic EL element (Reference 1: Japanese Patent Laid-Open No. 2003-282253).
Reference 1 discloses that, when dielectric breakdown occurs by performing aging treatment which applies voltage between an anode and a cathode of an organic EL element, the range of voltage to be applied between both electrodes is optimized. Specifically, it is disclosed to measure a current which flows by applying reverse bias voltage to the organic EL element and find breakdown voltage of the defective portion and that of the organic EL element, and then to make the voltage range of both breakdown voltages in the range of voltage applied in the aging treatment.
Reference 1 also discloses that a dedicated circuit for the aging is unnecessary since the aging can be performed using an ordinary driver circuit of the organic EL element.
The light emitting element has a problem of deterioration over time as well as initial deterioration, and variation in deterioration. Reference 1 discloses that oxygen as well as water is considered as a cause for generating a dark area that is a non-light-emitting region which progresses from a pixel edge over time, and an oxygen concentration in a filler gas used in the step of sealing the element is set equal to or less than that in the aging step.
Reference 1 also discloses a so-called passive type display panel in which an anode and a cathode are each formed in stripe shapes extending in mutually perpendicular directions. It further discloses that voltage applied for aging is selected from −8 V to −36 V.
However, applied voltage as described above may destroy a transistor in the case of an active type in which a transistor is connected to each light emitting element.